Consistent molecular changes associated with the transition of chronic myelocytic leukemia (CML) to blast crisis were not identified until an analysis of the p53 gene in human malignancies revealed a frequent association of alterations of p53 with blast crisis. The objective of this proposal is to determine the frequency and type of acquired alterations of the p53 gene in hematopoietic stem cells, and to relate these alterations to the progression of CML to the blast crisis phase. Rearrangements of the p53 gene are uncommon in hematological malignancies except in the blast crisis phase of CML. Utilizing nucleic acid hybridization, cytogenetic and immunoblotting techniques, correlations will be sought between structural alterations of the p53 gene and clinical parameters of CML including stage of disease, hematologic features phenotype of blast cells, and cytogenetic abnormalities. Alterations in the gene will also be looked for in related hematologic disorders including ph1 negative CML, Ph1 positive ALL and other evolving myeloproliferative disorders. The effects of altered p53 expression on the growth and diffentiation of hematopoietic cells will be examined utilizing expression vectors containing normal and altered p53 genes. The normal controls of p53 transcription will be examined utilizing DNA footprinting and protein expression assays, and aberrations of these control mechanisms will be sought in the clinical and clonal evolution of CML. Detection of acquired alterations of the p53 gene in CML cells may be useful in detecting the emergence of blast crisis and may be useful in the clinic for planning therapy.